Is it normal to act different around different people?

I behave this way. I think most (although not all) people do, whether they're aware of it or not. I'm very conscious of mirroring the way people around me speak and the thinks they say. Little turns of phrase new friends use tend to creep into my speech after I've got to know them well. When I try to explain this to other people they tend to think of me as a copycat as opposed to an interesting psychological observation, despite the fact that I can see them doing the same thing. Being so conscious of it is one of the burdens of being interested in psychology :P